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BIOL 1001 (162)
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Chapter 17

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BIOL 1001
Tamara Kelly

Chapter 17 Microevolution 2192012 21800 PM 171 Variation in Natural Populations Phenotypic Variation differences in appearance or function that are passed from generation to generation animals within a species can differ in anatomy and behavior this is caused by phenotypic variation Quantitative Variation when individuals differ in small incremental ways eg height of individuals amount of hair This is usually graphed as a bar and as a curve with a large sample Width of the curve is proportional to the variability mean describes the average value of the character Qualitative Variation they exist in two or more discrete states there is no intermediate between them eg geese can have either white or blue feathers there is no blending Polymorphism when there is discrete variant characters eg A B AB O blood types we calculate polymorphisms by calculating percent frequencies of each trait Phenotypic variation can be caused by genetic differences environmental factors or interaction between genetics and environment more likely Organisms with different genotypes can result in the same phenotype Organisms with the same genotype can result in different phenotypes as well ONLY GENETIC BASED VARIATION CAN CAUSE EVOLUTIONARY CHANGE How to determine what caused phenotypic variation Environmental Cause changes the environment and measures the effects of genetically similar species Genetic Cause determines through breeding quantitative variation will only respond to this method You can also construct pedigrees for humans Genetic Variation has two sources 1 Production of new alleles caused by mutations 2 Rearrangement of existing alleles caused by change in chromosomal structure genetic recombination during meiosis random fertilization The shuffling of existing phenotypes can cause a number of genotypes and phenotypes in the next generation The identification of a protein polymorphism allows to infer genetic variation at the locus coding for that protein Studies show that every locus exhibits variability in its nucleotide sequence Some variation may not affect phenotypes since they dont change amino acid sequences
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